1. Field of the Invention
The invention relates to highly resilient thermoplastic polymer blend compositions, their manufacture and their use as a substitute for thermoset and other materials, particularly in the manufacture of one-, two-, three-piece, and multi-layered golf balls. These compositions are also useful as foamed materials in footware and in other sport balls such as softballs.
2. Description of Related Art
Typically, thermoset materials such as polybutadiene rubber, cross-linked EVA, cross-linked SBS, and cross-linked urethanes have been used in applications where properties such as resilience, durability, and low hardness are needed. For example, polybutadiene rubber has traditionally been used in the cores and centers of golf balls.
There currently exist several types of premium golf balls, particularly three-piece balls, two-piece balls and multi-layered balls. “Three-piece” balls typically have a spherical molded center, having an elastomeric thread-like material wound around it, covered with either a thermoplastic or thermoset material. “Two-piece” balls typically have a spherical molded core covered with a thermoplastic material. “Multi-layered” balls typically have a core and one or more intermediate layers or mantles between the core and a cover.
The material used to mold the three-piece centers and the two-piece and multi-layer cores has traditionally been a thermoset rubber such as polybutadiene rubber. There are, however, major disadvantages in using thermoset rubbers such as the inability to recycle scrap materials and the need for complex multi-step manufacturing processes. There has been only limited success in attempts to replace the thermoset materials with more-easily-processed thermoplastic materials, the scrap of which can be recycled.
Also, three-piece balls, two-piece balls, and multi-layered balls are by their very nature more complicated and costly to manufacture than the long sought after one-piece golf ball. Attempts to make a premium one-piece ball have heretofore not been successful. Limited-flight range balls, however, have been produced from thermoset rubber and from certain thermoplastic material as set forth in U.S. Pat. No. 5,155,157.
U.K. Patent Application 2,164,342A describes one attempt to replace centers and cores and achieve a one-piece golf ball. It teaches moldable compositions comprising ionic copolymers (or potentially ionizable acid copolymers) blended with certain thermoplastic materials such as a polyether block copolyamide, polyether block copolyester and the like. Those compositions are said to be useful as three-piece centers, two-piece cores and one-piece solid golf balls, but they lack properties such as durability. Also, U.S. Pat. No. 5,155,157 describes a thermoplastic material for cores, centers and one-piece balls. The resins described in this patent can be molded into golf ball parts but the resulting balls are too hard and not resilient enough to perform as a premium golf ball and they are probably too expensive.
There still exists the need for a thermoplastic material that is resilient and durable enough with a low enough hardness or compression to be useful as a three-piece center, two-piece core, a one-piece golf ball, and in cores and mantles in a multi-layered golf ball in premium golf balls. In particular, there is a need for a thermoplastic material that provides economic advantages relative to the materials now known in the art.